Artificial leather



Patented July 24, 1934 UNITED STATES PATENT OFFICE ARTIFICIAL LEATHER No Drawing. Application August 9, 1932, Serial No. 628,110

2 Claims.

This invention relates to artificial leather products and more particularly to an impreg-.

nated and coated product which is especially adapted for the manufacture of automobile tops and upholstering material.

It has been customary in the manufacture of automobile top material to apply a rubber coating to a fabric base and then apply an asphalt top coating which is baked at a temperature sufliciently high to cause vulcanization of the rubber. It has also been suggested that the fabric might be replaced by a paper base, but, insofar as I am aware, a satisfactory artificial leather product made with a paper base and having'the necessary durability and flexibility and other properties most desired in automobile top material has not been produced.

This invention has as an object an improved artificial leather product which is inexpensive to manufacture and which possesses to an exceptional degree those properties which are most valuable in artificial leather products designed for use as automobile top material, upholstering material and similar types of artificial leather products.

These objects are accomplished by the following invention which in its more specific aspect consists in impregnating with rubber latex an absorbent paper or felt made from artificially crinkled cellulose paper pulp, applying a rubber coating, then applying a top coat of an asphalt coating composition and baking the resulting product.

The preferred method of carrying out my invention is given in the following examples.

The absorbent felt which I use as a base in the manufacture of my improved automobile top material is made in accordance with Patent 1,857,100 issued to F. H. McCormick and G. L. Schwartz. Briefly, this method consists in intimately' mixing or' dispersing paper pulp with caustic soda of mercerizing activity and separating the strong caustic from the pulp before the reaction has proceeded appreciably further than a superficial mercerization or skin efiect, the nonalpha cellulose constituents not being removed to any substantial extent, As soon as the fibers have been mixed with the causticsolution, the reaction is stopped immediately by diluting the caustic in contact with the fibers below mercerizing activity. After being washed the treated pulp is made into a felt. or paper with paper making machinery. The effect of time action of the strong caustic on the pulp is minimized by the use of low pulp consistencies; i. e., a small ratio of liquor to pulp. For most pulps the strength of the caustic soda solution should be above 8% and strengths higher than 35% are not desirable because of the poor wetting qualities of the solution, 10% to 24% at room temperature being preferred. The products most suitable for the practice of my invention are obtained from kraft or other pulps which have a mean fiber length of about 1.5 mm. to 4 mm. The artificially crinkled superficially mercerized pulp thus produced is distinguished from other pulps by its high freeness. the freeness value ranging from 15 seconds or less to about 40 seconds as determined by the special freeness tester described in the mentioned patent. The pulp constituting the base material of my new artificial leather product responds to the test for mercerized fibers in that the fibers when viewed in the microscope have a wiry or rod-like form as distinguished from the ribbon-like form of ordinary cellulose fibers. If the mercerizing agent used to crinkle the fibers is caustic soda the fibers also give a blue stain with zinc chloroiodine solution.

Example A sheet of artificially crinkled felted fibrous material-was made by treating kraft pulp with 18% sodium hydroxide in accordance with the procedure outlined above. The felt thus produced was impregnated with 15% rubber latex so that the final product contained 20% rubber. The impregnated and dried sheet was then coat- I ed with a rubber composition by calendering or spreading. .A thin coat of quick drying shellac varnish was then applied over the calender or spreader coat to remove the surface tack from the layer, which permits the material to be rolled up immediately. The material was then embossed in any suitable pattern by passing it through engraving rolls. Finally, the material was finished in a two-coat system which consists in applying a first coat of a flexible oil varnish, drying this coat at an elevated temperature but below the vulcanizing temperature of the rubber compound. This drying of the first coat varnish is usually accomplished by heating for a period of fifteen minutes at 250- 255 F., and then cooling. The final or top coatis an asphalt varnish applied in the usual manner and finished by baking at a temperature of 250-255 F. for such time as is required to complete the vulcanization of the rubber. A usual schedule being approximately 2 hours at The flexible oil under coat varnish and the asphalt top coat varnish referred to above are as follows:

Under coat Parts by weight Carbon black 3 Bodied China-wood oil and drier 22 Bodied linseed oil and drier 20 Turpentine substitute 55 Top coat Parts by weight Petroleum asphalt 20.00 Bodied China-wood oil 12.00 Turpentine substitute 68.00

' The asphalt is heated to 500 F., allowed to cool to 425 F., an equal weight of turpentine substitute is added, and the mixture is stirred until the asphalt is competely dissolved. To this solution, add a solution of China wood oil in turpentine substitute.

For many purposes, it is advantageous to use the somewhat denser, but still highly absorbent, base obtainable by hydrating in a special manner the caustic treated and artificially crinkled pulp referred to above. In preparing the hydrated mercerized pulp the caustic treatment is carried out as described above but preferably with the weaker solutions within the, mercerizing range, the minimum concentration being above 6.5% at room temperature. After the 'caustic treatment the pulp is beaten in water under conditions which do not cause any substantial reduction in the fiber length through cutting. To this end the beating in water is effected with the beater roll set at a light brushing position and the pulp is present in the aqueous .dispersion at a consistency about 4% to 5%, a

consistency somewhat higher than is conventional in ordinary processes involving the beating of pulp in water. By this means a continuous squeezing action isexerted on the pulp. In this treatment of the pulp the decrease in freeness from 60-31 seconds of the caustic treated kraft pulp (these freeness values being obtained with 6.5% and 14% sodium hydroxide, respectively) to a value within the range of, 85- 200 seconds is due to the hydrated condition of the pulp and not to diminution of the fiber length. This hydrated pulp responds to the tests for mercerized pulp referred to above and may further be identified as being hydrated by boiling in water to reverse the hydration as will be evidenced by the increase in freeness. The freeness of the hydrated pulp increases in freeness at least 15% when boiled in water for 15 minutes and in some instances a 90% increase in freeness is obtained.

Another variation in preparing the base material consists in cutting the crinkled fibers produced in accordance with the above mentioned patent until the shortening of the fiber length reduces the freeness within the range of 40 to seconds. Better sheet formation is facilitated by this means and although the absorb ency is decreased with the decrease in freeness of the pulp, the sheet, due to the wire-like nature of the crinkled fibers and their heterogeneous arrangement, possesses peculiar absorbent properties not possessed by paper made from ordinary pulps oi the same freeness range.

The mention of artificially crinkled fibers in the claims means specifically the artificially crinkled superficially mercerized paper pulp fibers produced as above described. I desire it to be understood, however, that the above-described absorbent paper per se forms no part of the present invention and no claims are made thereto except insofar as it is an element in the combination which constitutes my improved artificial leather product.

Under certain conditions of outdoor exposure, the rubber impregnated sheet or felted crinkled fibers produced as described above has some tendency to absorb water and swell. I have found that this tendency may be overcome by curing the latex either by the action of sulphur chloride vapor on the impregnated product or by incorporating curing agents in the latex prior to impregnation.

The rubber latex may be used in its normal concentration or in a concentrated or in' a thickened form. Dispersions containing from 10- 60% solids, but preferably Iii-40%, may be used. Synthetic latices may also be used.

In carrying out my invention, I may use either a one-coat or a two-coat varnish system as exemplified in the example and these systems may be either air-dried or baked. It is highly desirable to bake the varnish because of the durability (retention of luster) obtained when the finishes are baked. Two-coat varnish systems are generally preferable because of the 'bufier or bridge action of the flexible intermediate varnish coat. In the preparation of the varnishes used in the present invention, either blown or steam refined asphalts may be used, but steam refined asphalts are generally preferred because of the combination of low penetration and high melting points which are possessed by these asphalts, and because products having superior durability are usually obtained through the use of steam refined asphalts. The varnishes employed in the processes of the invention may consist of straight asphalt solutions, mixtures of asphaltic materials with drying oils in suitable solvents, mixtures of asphalt with drying oil modified polyhydric alcohol-polybasic acid resins in suitable solvents, or mixtures of asphalt with drying, semi-drying, or non-drying oil acids in suitable solvents. In the case of the asphalt-drying oil acid varnishes, the oils or oil acids may be used either untreated, heat-treated, or blown.

When China-wood oil is used as a component of the oil-asphalt varnish, the China-wood oil should be heat-treated sufilciently to prevent wrinkling of the varnish coating. Special care must also be taken not to body the oils (especially linseed oil) too highly in order to avoid difliculty with regard to incompatibility of the asphalt-drying oil systems. In the case of asphalt-drying oil modified polyhydrlc alcoholpolybasic acid resin varnishes, it is generally preferable to use resins of relatively high acid numbers (20-50) in order to avoid 'difliculty with regard to incompatibility of the asphaltoil modified polyhydric alcohol-polybasicacld resin systems. However, if these oil modified resins are further modified with rosin or other viscosity reducing agents, the acid number can be considerably reduced without danger of incompatibility of the asphalt resin systems.

The varnishes described herein may be used either with or without driers or blending agents,

such as the resinates, linoleates, or oleates of cobalt, lead, manganese, and iron or mixtures of these materials. However, in most cases, it is preferred to use the oleate or resinate of iron because of the superior retention of luster which is realized with systems containing these agents.

Products prepared in accordance with the present invention are of exceptional utility in the manufacture of automobile tops, particularly of the panel deck variety, for upholstery material, luggage materials, seat coverings, and other uses for which artificial leather is adapted. Sheets of the artifically crinkled material may be laminated with cloth, other sheets of the same or difi'erent varieties of the artifically crinkled material or even with wire gauze or screen material before, during, or after impregnating prior to the coating of the top sheet of artifically crinkled material with the varnishes described herein.

Automobile top material consisting of the felted base, impregnated with rubber latex, and then varnished with the asphalt varnish compositions previously described is markedly superior in appearance to the systems in which cloth is used. This superior appearance is due to the fact that thesurface of these felted, fibrous sheet systems shows no evidence of woven structure such as is present in coated textile fabric materials. Furthermore, in the case of the usual coated textile fabric materials, a comparatively thick coat of rubber is necessary in order to obscure the surface structure of the textile fabric. comparatively thin coats of rubber can be used in the practice of the present invention and therefore cheaper, more flexible products can be obtained which have a much more leathery feel than similarly coated textile fabrics. A smoother, more uniform coating of varnish can be obtained over the smooth leathery surface of this coated fibrous base material than over the comparatively rough surface of coated textile fabrics. Among the many advantages of this smooth varnish coating, particular reference may be had to the superior appearance, improved adhesion, decreased tendency to fiake or shatter (probably due to the thinness and uniformity of the coating which is realized in these systems), and a decrease in tendency to accumulate dust or dirt.

The especially prepared base described herein is particularly suited for the present invention because of its crinkled nature and felty structure. The firm bonding of the coating to the base materiaL'made possible by the practice of the present invention, is a particularly desirable property for leather-like products which are to be used as automobile top material. The collapsibility of my improved automobile top material is highly advantageous, as folding of the coated product subjects the surface film to a much small strain when folded than in the case of other paper products similarly treated.

As many apparently widely different embodiments of this invention may be made without departing from thespirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the following claims:

I claim:

1. A process for manufacturing artificial leather which comprises impregnating a felt of artificially crinkled mercerized paper-making fibers with an aqueous dispersion of rubber, applying a coating of unvulcanized rubber over the impregnated felt, applying a final coat of asphalt varnish, and baking the resulting product.

2. A flexible artificial leather product comprising a felt of artificially crinkled mercerized paper-making fibers impregnated with rubber latex, a rubber coating on the impregnated felt, and top coat of dried asphalt varnish.

MAX N. NICKOWITZ. 

